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Skelton, P. W. 2013. Rudist classification for the revised Bivalvia volumes of the ‘Treatise on Invertebrate Paleontology.’ Caribbean Journal of Earth Science, volume 45, 9-33. © Geological Society of Jamaica. Available online 12th March 2013. Rudist classification for the revised Bivalvia volumes of the ‘Treatise on Invertebrate Paleontology’ PETER W. SKELTON Department of Environment, Earth and Ecosystems, The Open University, Milton Keynes MK7 6AA, UK ([email protected]) ABSTRACT. An updated phylogenetic classification of rudist bivalves is proposed for the revised Bivalvia volumes of the ‘Treatise on Invertebrate Paleontology’. Already formalised as Order Hippuritida Newell, rudists are divided between two new monophyletic suborders established herein, Requieniidina, comprising all taxa attached by the left valve, and Radiolitidina, encompassing all those attached by the right valve. The Requieniidina contains one superfamily, Requienioidea Kutassy, consisting of a small paraphyletic family, Epidiceratidae Renngarten, and a larger derivative family, Requieniidae Kutassy. The Radiolitidina contains two superfamilies re-defined herein, Radiolitoidea d’Orbigny and Caprinoidea d’Orbigny. The paraphyletic Radiolitoidea includes a small basal family, Diceratidae Dall, together with a major clade that encompasses the paraphyletic Monopleuridae Munier Chalmas and a large descendent family, Radiolitidae d’Orbigny, as well as a smaller descendent family, Polyconitidae Mac Gillavry, which, in turn, is considered the root stock for the families Plagioptychidae Douvillé, Hippuritidae Gray, Caprotinidae Gray, Caprinulidae Yanin, and Trechmannellidae Cox. The monophyletic Caprinoidea d’Orbigny, comprises the monophyletic Family Caprinidae d’Orbigny and paraphyletic Family Caprinuloideidae Damestoy, from which probably arose both the families Ichthyosarcolitidae Douvillé and Antillocaprinidae Mac Gillavry. This classification covers at least 158 genera (including a few currently being described), leaving 8 poorly known genera as incertae sedis. A glossary of morphological terms is appended. Key words: Bivalvia, Rudists, Phylogenetic classification, Order Hippuritida, Suborder Requieniidina, Suborder Radiolitidina. 1. INTRODUCTION and their ancestral ‘stem groups’ that lack the diagnostic shared derived characters The suprageneric classification of rudists set out (synapomorphies) of the former are unavoidably below is proposed for the revised Bivalvia volumes assigned to different higher taxa of equivalent rank of the ‘Treatise on Invertebrate Paleontology’, (Carter et al., 2011) – as in the analogous vertebrate currently in preparation. It is a revision of that case of birds and reptiles. Taxa considered to given in Carter et al. (2011) following presentation include the ancestors of other named taxa of of the latter scheme by the author at the 9th equivalent rank are, by definition, paraphyletic, and International Congress on Rudists, held in are indicated here by ‘!’ after the taxon name, Kingston, Jamaica, in June 2011, and subsequent following the convention used in Carter et al. discussion at the meeting and thereafter. It includes (2011). In order to optimise the phylogenetic previous nomenclatural corrections by Bouchet et informativeness of the classification set out here, al. (2010) according to the articles of the paraphyletic families of stem group genera have International Commission on Zoological been kept as small as current phylogenetic Nomenclature (ICZN; Ride et al., 1999). resolution allows – although scope certainly Most of the suprageneric taxa presented here remains for further pruning with more probing are monophyletic, according to current phylogenetic analysis. Polyphyletic taxa, which phylogenetic analyses (e.g., Skelton and Masse, misrepresent evolutionary relationships by pooling 1998; Chartrousse, 1998a; Skelton and Smith, together taxa of independent ancestry, have been 2000; Masse, 2002; Scott et al., 2010). The avoided, as far as present understanding allows. establishment of such taxa is the main goal of Additional nomenclatural and systematic notes, phylogenetic systematics because they concerning, for example, junior synonyms, unambiguously reflect the hierarchy of inferred authorship, publication dates, or amended contents evolutionary branching events (Smith, 1994). (indicated by ‘zoological taxon revised herein’), are When classifying fossil organisms according to the added after some taxa, in square brackets [thus]. Linnean system, however, novel grade-groupings Diagnostic characters are noted for each 9 Peter Skelton. Classification of the Rudist Bivalves suprageneric taxon, with key synapomorphies for 2. RUDIST CLASSIFICATION SINCE DECHASEAUX monophyletic taxa asterisked (*) – though ET AL., 1969 allowance must be made for exceptions due to 2.1 Improvement of the phylogenetic basis secondary modification (just as snakes are regarded as ‘tetrapods’, despite lacking legs). Paraphyletic The history of work on rudist phylogeny and the taxa, by contrast, are necessarily diagnosed by their defects of the first ‘Treatise…’ classification of retained primitive character states. Phylogenetic rudists (Dechaseaux et al., 1969) in that respect explanations, additional derived characters found in were discussed by Skelton and Smith (2000). The some constituent genera and palaeoecological or latter authors’ cladistic analysis revealed a distributional attributes of given taxa are appended fundamental phylogenetic dichotomy between under ‘Comments’. Doubts over the higher rudists attaching by the LV and those attaching by taxonomic assignments of genera that are the RV that divides even the paraphyletic nevertheless validly established are indicated by a Diceratidae Dall, 1895, as conceived by single query mark (‘?’). Published taxa that remain Dechaseaux et al., (1969), confirming Douvillé’s of questionable status (e.g., perhaps diagnosed on (1935) postulate of two evolutionary branches insufficient evidence, and/or possible candidates issuing from Epidiceras and Diceras. These two for synonymy with other genera) are indicated with clades are formally established herein as new double query marks (‘??’). suborders, Requieniidina (Section 3.2) and Bibliographic references for the majority of Radiolitidina (Section 3.3), respectively. They taxon authorships cited here are given in Thomas should not be confused with the ‘Dextrodonta’ and Steuber’s (2002) invaluable website resource ‘A ‘Sinistrodonta’ of Pchelintsev (1959), which, as palaeontological database of RUDIST BIVALVES’ their names indicate, are based instead upon (http://www.paleotax.de/rudists/intro.htm/Taxonom dentition, the first group possessing what Douvillé ic Database/Publications), so are not repeated here (1887) had termed ‘normal dentition’ (two main unless pertinent to further discussion. teeth in the RV and one in the LV) and the second, Ongoing taxonomic descriptions and ‘inverse dentition’ (two in the LV, and one in the phylogenetic analyses will undoubtedly require still RV). Pchelintsev’s (1959) suborders are thus further revision both to the classification and separated at the transition between Diceras and (especially) to diagnoses before final publication in Valletia within the Radiolitidina. Taxonomic the revised Bivalvia volumes of the ‘Treatise…’, division between the consequently paraphyletic and rudist workers are encouraged to submit Dextrodonta and monophyletic Sinistrodonta is proposed additions and/or amendments to the rejected here in favour of the two monophyletic scheme for discussion among the rudist working sister groups established below. Also rejected is group – copied, please, to the author. It is over Mainelli’s (1992) attempt to revise Pchelintsev’s forty years since the publication of the first (1959) suborders in order to reconcile them with ‘Treatise…’ classification of rudists (Dechaseaux et Douvillé’s (1935) dichotomy by isolating Diceras al., 1969). Building on the substantial progress that in a monogeneric suborder, ‘Dicerasodonta’. has been made since then, thanks especially to the Besides the extreme taxonomic imbalance involved nine international rudist congresses held from 1988 in Mainelli’s (1992) tripartite subordinal scheme, to 2011, we should now aim to furnish a workable and the confusion of derived characters (concerning scheme that will still be regarded as a reliable both dentition and valve of attachment) from reflection of rudist phylogeny in another four different phylogenetic nodes in his diagnoses, the decades. names employed by Mainelli are also unacceptable Abbreviations for morphological features used because they are not taxon-based, contrary to the throughout are listed in Table 1 (see also protocol agreed for the classification of the Bivalvia Appendix 1 for a glossary of terms). adopted by Carter et al. (2011). A comprehensive classification of rudists has Table 1. Abbreviations used for also been proposed by Yanin (1990; 1995), in which morphological features of rudists a large number of new suprageneric taxa were am anterior myophore introduced. However, many of the groupings at anterior tooth recognized by him are polyphyletic according to the ct central tooth LV left valve phylogenetic analyses followed here, while the ol outer shell layer numerous monogeneric subfamilies or even families pm posterior myophore included are phylogenetically uninformative. pt posterior tooth Moreover, his two suborders ‘Diceratina Yanin, RV right valve 1989’ and ‘Hippuritina Newell, 1965’,